Sheet feeding apparatus

ABSTRACT

A sheet feeding apparatus including a stacking portion for stacking a plurality of sheets thereon, a sheet feeding portion for feeding the sheets stacked on the stacking portion, a fan for sending air to the sheets to loosen the sheets stacked on the stacking portion, a heater for warming the air sent by the fan, a temperature detecting portion for detecting the temperature of the heater, and a control portion for starting the driving of the fan in conformity with the temperature detecting portion having detected a predetermined temperature after temperature control for adjusting the heater to a target temperature has been started.

This application is a divisional of U.S. patent application Ser. No.10/923,741, filed Aug. 24, 2004, now allowed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a sheet feeding apparatus for sending warm airto a sheet to be fed.

2. Related Background Art

There has been proposed a construction for flowing warm air againstpaper in a sheet feeding paper deck mounted on an image formingapparatus such as a copying machine to thereby loosen the paper (forexample, Japanese Patent Application Laid-Open No. 2001-048366).

In this example of the prior art, basically the temperature controllingoperation of an air heater and a sheet loosening operation (for example,the start of fan rotation and the start of swing shutter motor rotation)are started at a time. That is, the fan starts rotation simultaneouslywith the start of the temperature control of the air heater.

Therefore, much time is required until the air heater temperature, i.e.,warm air temperature assumes a predetermined value, and this leads tothe disadvantage that the time until the loosening operation isterminated and the sheet feeding operation becomes possible is slow witha result that the performance of the entire apparatus is lowered.

Also, in order to avoid the above-noted disadvantage peculiar to theabove-described example of the prior art, there is conceivable aconstruction for starting the loosening operation before the air heatertemperature reaches the predetermined value, but in this case, theloosening operation (air assisting operation) is started before the warmair temperature rises sufficiently, and this leads to the disadvantagethat loosening becomes insufficient.

Generally, in an air assisting construction wherein warm air is blownagainst the sheets in the paper deck to thereby loosen the sheets toreliably loosen the sheets, it is necessary to flow warm air of apredetermined temperature or higher for a predetermined value of time orlonger, and flowing air of a temperature lower than the predeterminedtemperature is little effective for the loosening of the paper. Also, incase of blowing an air of low temperature against the sheets of paper,the sheets of paper may get damp. As a result, this may affect theloosening operation, and deteriorate quality of images to be formed onthe sheets of paper.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a sheet feedingapparatus which has eliminated the above-noted inconveniences and acontrolling method therefor.

It is another object of the present invention to provide a sheet feedingapparatus which can quickly and reliably effect the loosening of sheetsand can accurately convey the sheets and a controlling method therefor.

Other objects of the present invention will become apparent from thefollowing description based on the accompanying drawings and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a paper deck according to a first embodiment of the presentinvention.

FIG. 2A shows heater temperature and warm air temperature in a case notaccording to the first embodiment.

FIG. 2B shows heater temperature and warm air temperature in a caseaccording to the first embodiment.

FIG. 3 shows a paper deck according to a second embodiment of thepresent invention.

FIG. 4A shows heater temperature and warm air temperature in a case notaccording to the second embodiment.

FIG. 4B shows heater temperature and warm air temperature in a caseaccording to the second embodiment.

FIG. 5A shows a chart for determining the target temperature of an airheater 14 in the case of coat paper.

FIG. 5B shows a chart for determining the target temperature of the airheater 14 in the case of non-coat paper.

FIG. 6 is a control flow chart of a controller 16.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

In FIG. 1, an image forming apparatus 1 effects image forming on a sheet7 supplied from a paper deck 4. A pickup roller 5 is rotated to therebyfeed the uppermost one of a plurality of sheets 7 stacked on the paperdeck 4 toward the image forming apparatus 1.

A sheet detecting sensor 8 detects the thickness, density (basis weight)and size of the sheet 7 and sends information to a controller 16.Besides the detection by the sheet detecting sensor 8, a user can alsoinput information regarding the sheet from the operating portion or thelike of the image forming apparatus 1.

A temperature detecting sensor 9 and a humidity detecting sensor 10detect the temperature and humidity of the interior of the paper deck 4,and send this information to the controller 16.

A fan 11 blows warm air against the vicinity of the uppermost one of thestacked sheets and loosens the sheet 7 to thereby prevent the doublefeeding of the sheets. A swing shutter 19 is reciprocally moved, forexample, in a vertical direction, and partly intercepts or passes thewarm air from the fan 11 to thereby loosen the sheet 7. The swingshutter 19 is driven by a swing motor (not shown).

A duct 13 has an air heater 14 therein. In this embodiment, air is takenin from the lower portion of the duct 13, and the air warmed by the airheater 14 is exhausted by the fan 11.

An AC voltage 18 is supplied to the air heater 14 by the controller 16through the ON/OFF control of a solid state relay (SSR) 17, and forexample, a resistor included in the air heater 14 generates heat tothereby warm the air taken in from the lower portion of the duct 13.

An air heater temperature detecting sensor 15 is in contact with the airheater 14 and sends information regarding the temperature of the airheater 14 to the controller 16. The controller 16 effects temperaturecontrol through the AC voltage 18 and the ON/OFF control of the SSR 17on the basis of the information from the air heater temperaturedetecting sensor 15 so that the temperature of the air heater 14 mayassume a predetermined value.

Description will hereinafter be made of the operation until in theabove-described construction, the air heater 14 starts temperaturecontrol to thereby loosen the sheets 7 and the pickup roller 5 startssheet feeding. FIG. 6 shows a control flow chart of the controller 16.

First, information regarding the kind, thickness, density and size ofthe sheet is obtained from the sheet detecting sensor 8 or the operatingportion (step S61). An optimum target air heater temperature isdetermined on the basis of the temperature information and humidityinformation sent form the temperature detecting sensor 9 and thehumidity detecting sensor 10, respectively, to the controller 16, andthe information regarding the kind, thickness, density and size of thesheet sent from the sheet detecting sensor 8 or the operating portion tothe controller 16. The controller 16 determines the target air heatertemperature on the basis of a program for executing a judgment flowcorresponding to charts shown in FIGS. 5A and 5B (step S62).

For example, let it be assumed that the sheet detecting sensor 8 hasdetected that the kind of the sheet is coat paper, the temperaturedetecting sensor 9 has detected 25° C. and the humidity detecting sensor10 has indicated 70%. In that case, the controller 16 determines theoptimum target air heater temperature to be 90° C.

In a case where the controller 16 temperature-controls the air heater14, when the information from the air heater temperature detectingsensor 15 indicates a temperature less than 90° C., the SSR 17 isswitched on to thereby electrically energize the air heater 14 andraises the temperature of the air heater, and when the aforementionedinformation indicates 90° C. or higher, the SSR 17 is switched off andthe air heater 14 is not electrically energized.

In the case of non-coat paper, the heater is always turned off.

The subsequent operation will be described with reference to FIGS. 2Aand 2B. FIG. 2B shows the operation of the present embodiment. The axisof abscissas indicates time, and the axis of ordinates indicatestemperature, and the graph shows the temperature of the air heater 14(the output of the air heater temperature detecting sensor 15) and thewarm air temperature. The arrows in FIGS. 2A and 2B indicate a triggerrelation.

The warm air temperature is the temperature of the air at a point A inFIG. 1. Although in present embodiment, the temperature detecting sensoris not provided at the point A, there is shown the state of the warm airtemperature at the point A when the temperature of the air heater 14 issuch a curve as shown in FIG. 2B.

First, the controller 16 starts the temperature control of the airheater 14 at the timing of T=0. At this point of time, the fan 11 is notrotated, nor the swing shutter 19 is operated.

Thereby, the temperature of the air heater 14 rises and reaches an airheater target temperature at timing T1.

In FIG. 6, whether the temperature of the air heater has reached thetarget temperature is judged (step S63), and when it reaches the targettemperature, the controller 16 starts the rotation of the fan 11 (stepS64). At this point of time, however, the swing shutter 19 is notoperated.

Thereby, the warm air temperature rises and reaches a warm air finaltemperature at timing T2. Here, for the first time, the controller 16operates the swing shutter 19, and the air of the warm air finaltemperature is flown against the vicinity of the uppermost one of thesheets 7 whereby the sheets are loosened. During the time between T1 andT2, the heater temperature overshoots undershoots, but actually the timefrom T1 till T2 is short and therefore, there is little or no influenceupon the warm air temperature.

Accordingly, the sheet loosening operation is started from the timingT2. The warm air temperature at this time has reached the warm air finaltemperature and the warm air has become warm air of a predeterminedtemperature from the beginning of the loosening operation.

The time necessary for loosening when this warm air of the predeterminedtemperature is flown is TS. That is, the loosening operation iscompleted at timing T3 whereat the time TS has elapsed from the timingT2, and it is possible to start the sheet feeding operation (to rotatethe pickup roller 5) from the timing T3.

In air assist wherein warm air as flown against the sheets in the paperdeck to thereby loosen the sheets, to loosen the sheets reliably, it isnecessary to flow warm air of a predetermined temperature or higher forthe predetermined time TS or longer, and flowing air of a temperaturelower than the predetermined temperature is little effective for theloosening of the sheets.

Here, the state when unlike the present embodiment, the rotation of thefan 11 has been started with the start of the temperature control of theair heater 14 will be described with reference to FIG. 2A. At the timingof T=0, the temperature control of the air heater 14 is started andsimultaneously therewith, the rotation of the fan 11 is started. It isto be understood that at this time, the swing shutter 19 is notoperated.

Thereupon, the air of a low temperature from the lower portion of theduct 13 introduced by the rotation of the fan 11 hampers the temperaturerise of the air heater 14 and therefore, the rising speeds of the heatertemperature and warm air temperature are lower than in the presentembodiment (FIG. 2B), and it is after timing T4 later than T2 that theheater temperature reaches the air heater target temperature.

Then, the swing shutter 19 is operated from the timing T4 and barely theoriginal loosening operation becomes possible and therefore, it is attiming T5 whereat a time TS has elapsed from the timing T4 that theloosening operation is completed. For the first time at the timing T5,the sheet feeding operation becomes possible and therefore, as comparedwith the present embodiment, the time when sheet feeding becomespossible is late, and an improvement in the productivity of the entireapparatus cannot be expected.

Also, there is conceivable a method of starting the loosening operationbefore the heater temperature reaches a target temperature, i.e., amethod of operating the swing shutter 19 from T=0 (or somewhere betweenT=0 to T=4, instead of operating the swing shutter 19 from the timingT4, but in this method, the loosening operation is started before thewarm air temperature rises sufficiently and therefore, loosening becomesinsufficient.

As previously described, generally, in the air assist wherein warm airis blown against the sheets in the paper deck to thereby loosen thesheets, to loosen the sheets reliably, it is necessary to flow warm airof the predetermined temperature or higher for the predetermined timeTS, and flowing air of a temperature lower than the predeterminedtemperature is little effective for the loosening of the sheets. Also,in case of blowing an air of low temperature against the sheets ofpaper, the sheets of paper may get damp. As a result, this may affectthe loosening operation, and deteriorate quality of images to be formedon the sheets of paper.

Accordingly, by controlling as in the present embodiment as previouslydescribed, it becomes possible to effect reliable loosening of thesheets within the shortest time.

That is, the air assisting operation (the rotation of the fan and therotation of the swing shutter motor) is started, after the air heaterhas assumed a predetermined temperature or higher, or after apredetermined time has elapsed after the air heater has assumed thepredetermined temperature or higher and therefore, warm air of apredetermined temperature can be made more quickly, and the looseningoperation can be terminated earlier to thereby bring about a state inwhich sheet feeding is possible.

Second Embodiment

A second embodiment is shown in FIG. 3. Chiefly the differences of thisembodiment from the first embodiment will hereinafter be described. Inthe second embodiment, a warm air temperature detecting sensor 12 isprovided at the point A of FIG. 1 in the first embodiment. The warm airtemperature detecting sensor 12 sends information regarding thetemperature of the warm air to the controller 16. While in the firstembodiment, the timing for the start of the loosening operation has beeneffected by the detection of the heater temperature, in the secondembodiment, it is effected by a value from the warm air temperaturedetecting sensor 12.

The time description of the above-described operation is shown in FIGS.4A and 4B. Basically, it is the same as the operation shown in FIGS. 2Aand 2B, but the trigger of the start of the loosening operation is notthe heater temperature detected by the air heater temperature detectingsensor 15, but the warm air temperature detected by the warm airtemperature detecting sensor 12. Thereby, the accuracy of thetemperature of the air blown against the uppermost one of the sheets 7,and the control or the like of the loosening time can be effectedaccurately, and it is possible to further improve the looseningperformance of the whole.

The present invention is not restricted to the above-describedembodiments, but various modifications one possible within the scope ofthe invention shown in the appended claims.

This application claims priority from Japanese Patent Application No.2003-308783 filed on Sep. 1, 2003, which is hereby incorporated bereference herein.

1. A sheet feeding apparatus comprising: a stacking portion which stacksa plurality of sheets thereon; a sheet feeding portion which feeds thesheets stacked on said stacking portion; an air sending portion whichsends air to the sheets to loosen the sheets stacked on said stackingportion; a heater which heats the air sent by said air sending portion;and a controller which controls said air sending portion and said heaterso that after a temperature adjustment of said heater has been started,an air sending operation to send air to the sheets is started.
 2. Asheet feeding apparatus according to claim 1, wherein said controllercontrols said air sending portion to start said air sending operation atpredetermined timing after said temperature adjustment of said heaterhas been started.
 3. A sheet feeding apparatus according to claim 2,wherein said controller controls the heater so that a temperature ofsaid heater becomes a target temperature, and said target temperature isdetermined on the basis of the information of at least one of a kind,thickness, basis weight and size of the sheets.
 4. A sheet feedingapparatus according to claim 2, wherein said controller controls theheater so that a temperature of said heater becomes a targettemperature, and said target temperature is determined on the basis ofthe information of peripheral environmental information of said sheetfeeding apparatus.
 5. A sheet feeding apparatus according to claim 4,wherein said environmental information is temperature or humidity.
 6. Asheet feeding apparatus according to claim 1, wherein said controllercontrols said air sending portion to start said operation after atemperature of the heater becomes a predetermined temperature.
 7. Asheet feeding apparatus according to claim 1, wherein said controllercontrols the heater so that a temperature of said heater becomes atarget temperature, and said controller controls said air sendingportion to start said air sending operation after the temperature of theheater become the target temperature.
 8. A sheet feeding apparatusaccording to claim 7, wherein said target temperature is determined onthe basis of the information of at least one of a kind, thickness, basisweight and size of the sheets.
 9. A sheet feeding apparatus according toclaim 7, wherein said target temperature is determined on the basis ofthe information of peripheral environmental information of said sheetfeeding apparatus.
 10. A sheet feeding apparatus according to claim 9,wherein said environmental information is temperature or humidity. 11.An image forming apparatus comprising: a stacking portion which stacks aplurality of sheets thereon; a sheet feeding portion which feeds thesheets stacked on said stacking portion; an image forming portion forforming an image on a sheet fed by said sheet feeding portion; an airsending portion which sends air to the sheets to loosen the sheetsstacked on said stacking portion; a heater which heats the air sent bysaid air sending portion; and a controller which controls said airsending portion and said heater so that after a temperature adjustmentof said heater has been started, an air sending operation to send air tothe sheets is started.
 12. An image forming apparatus according to claim11, wherein said controller controls said air sending portion to startsaid air sending operation at predetermined timing after saidtemperature adjustment of said heater has been started.
 13. An imageforming apparatus according to claim 12, wherein said controllercontrols the heater so that a temperature of said heater becomes atarget temperature, and said target temperature is determined on thebasis of the information of at least one of a kind, thickness, basisweight and size of the sheets.
 14. An image forming apparatus accordingto claim 12, wherein said controller controls the heater so that atemperature of said heater becomes a target temperature, and said targettemperature is determined on the basis of the information of peripheralenvironmental information of said sheet feeding apparatus.
 15. An imageforming apparatus according to claim 14, wherein said environmentalinformation is temperature or humidity.
 16. An image forming apparatusaccording to claim 11, wherein said controller controls said air sendingportion to start said air sending operation after a temperature of theheater becomes a predetermined temperature.
 17. An image formingapparatus according to claim 11, wherein said controller controls theheater so that a temperature of said heater becomes a targettemperature, and said controller controls said air sending portion tostart said air sending operation after the temperature of the heaterbecomes the target temperature.
 18. An image forming apparatus accordingto claim 17, wherein said target temperature is determined on the basisof the information of at least one of a kind, thickness, basis weightand size of the sheets.
 19. An image forming apparatus according toclaim 17, wherein said target temperature is determined on the basis ofthe information of peripheral environmental information of said sheetfeeding apparatus.
 20. An image forming apparatus according to claim 19,wherein said environmental information is temperature or humidity.